特约文章：复杂隧道围岩结构稳定性及其控制

作为隧道设计的核心问题，隧道围岩稳定性一直是隧道工程界研究的热点问题之一，能否对其准确评价是隧道穿越复杂地质条件安全施工的重要前提。针对该问题，首先通过模型试验对隧道围岩渐进破坏特征进行研究，指出围岩失稳破坏的阶段性特点，并通过对围岩失稳机理的分析，建立了隧道围岩失稳力学模型，提出了围岩失稳范围的确定方法。基于围岩失稳模式，将隧道围岩按其稳定性特点划分为浅层围岩和深层围岩，建立了复合隧道围岩结构模型，揭示了隧道围岩失稳的阶段性本质上是由深层围岩的分组运动所致，并就其结构稳定性特点进行了分析。考虑到地层条件的复杂多变，进一步对不同地层条件下复合围岩结构的表现形式进行了系统研究，提出了砂性围岩的“复合拱”效应和层状围岩的“梁式拱”结构型式以及“多层拱”效应，指出了各自的稳定性特点。最后，提出了复杂隧道围岩稳定性控制原理，研究成果可为隧道安全施工和支护设计提供理论依据。

Structural stability of complex tunnel surrounding rock and its control

Stability of tunnel surrounding rock, a core issue in underground tunnel design, has been a hot research field in tunnel engineering, and an accurate assessment of the stability is an important precondition for construction safety under complicated geological conditions. Aiming at this issue, first we conduct laboratory tests of tunnel surrounding rock to examine its behaviors of gradual destruction and reveal its staged development characteristics of instability and failure. Then, through analysis of the instability mechanism, a mechanical model of tunnel surrounding rock instability and a method for calculating the instability thresholds are developed. According to its stable behaviors and instability modes, tunnel surrounding rock is divided into inner and outer layers, and thus a compound surrounding rock structure model can be constructed. This study reveals that its developing stages of instability are essentially a consequence of the outer surrounding rock moving in a mode of grouping, and the characteristics of its structure stability are thus analyzed. For application to complicated and variable ground conditions, a systematic study is carried out focusing on the structure of composite surrounding rock in different stratigraphic conditions, and it shows the "composite arch" effect of the sand surrounding rock and the "beamed arch" structure and "multi-layer arch" effect of layered surrounding rock, together with the stability characteristics of these types of surrounding rock. Finally, a new stability control technology of complicated tunnel surrounding rock is presented in this paper. This study lays a theoretical basis for safety of tunnel construction and design of tunnel support.